1. Field of the Invention
The present invention relates to a digital/analog indication unit which is capable of performing both digital and analog indications of a detected value such as vehicle speed or the like, respectively by displaying numerals and rotating an indication needle on a scale.
2. Description of the Invention
Conventional systems include a so-called head-up display device for indicating driving information such as vehicle speed or the like, wherein an indicated image is projected within the visual field of the driver or the nearby area thereof in order to improve the visibility of the projected image even in a vehicle in motion.
For example, conventional system may include a device in which an image, which is indicated by an indicator such as a fluorescent display tube or the like, is projected first to a windshield or to a trans-reflective mirror disposed on a dashboard and thereafter reflected therefrom towards the driver's visual point, so that the driver can visibly observe the illuminated image of the vehicle speed or the like superimposed on the external view within the visual field of the windshield.
There has also been provided another type of vehicle indication unit in which an image such as vehicle speed displayed by an indicator is reflected by a reflecting mirror or the like provided at the lower side of the windshield, so that the reflected image is observed at the nearby region of the windshield.
An indicator for use with such heads-up display devices should preferably be a light-emitting type, so that the current speed can be immediately recognized, and for this reason, there have been proposed many digital indicators such as a fluorescent display tube or the like which are capable of displaying numerals by light-emitting segments.
With the digital indication as disclosed above, since the resolving power thereof is settled per each 1 Km/h the precision of measurement is determined by the precision of the clock pulse within a digital activation circuit+a(Km/h), and the hysteresis for suppressing the flickering of indication+b(Km/h) is provided, then the indication error is made to be+a+b(Km/h) as a result.
On the other hand, an analog-type indicator having an indication needle and a dial plate is often used for a speedometer disposed at an instrument panel. This analog-type indicator has conventionally been provided with an ammeter, a cross-coil or the like as an activator for rotating the indication needle and the activator is activated by an analog or digital circuit or by a combination thereof.
Since there are differences in factors and levels of error between a digital indicator used for a head-up display device and an analog indicator provided at the position of an instrument panel, and there is a difference between the activation circuits thereof, it has been difficult to reduce the mutual discrepancy in the indications therebetween.